Bimodal precipitate-strengthened NiCoCrMoW multi-principal element alloy synergizing strength-ductility at ambient and cryogenic temperatures

We developed a novel L1₂-strengthened Ni₄₇Co_26.5Cr₁₂Al₅Ti_4.5Mo₃W₂ (at.%) multi-principal element alloy (MPEA) by incorporating Al and Ti elements. Dual-modal precipitates, introduced by post-deformation annealing and aging treatments, endow this alloy with an exceptional combination of strength and ductility. In addition to the high density L1₂ precipitates with an average diameter of 37.8 nm dispersed within the matrix, larger L1₂ precipitates (average diameter: 416.5 nm) were observed in certain regions. These larger precipitates effectively inhibited recrystallization and subsequent grain coarsening process, resulting in a finer grain structure. The unique microstructure contributed to the remarkable mechanical properties of this alloy at ambient temperature (298 K), with a yield strength of 1124±19 MPa, an ultimate tensile strength of 1494±24 MPa, and a total elongation of 29.3±1.2%. Furthermore, under cryogenic conditions (77 K), this alloy demonstrated synergistic improvements in both strength and ductility, with a yield strength of 1263±11 MPa, an ultimate tensile strength of 1893±17 MPa, and a total elongation of 43.1±2.1%. These exceptional properties were attributed to the activation of high-density dislocations, stacking faults, and Lomer-Cottrell locks, along with their interactions with the dual-modal precipitates. Our findings provide valuable insights into the deformation and strengthening mechanisms of dual-modal precipitates-strengthened alloys and confirm that introducing dual-modal precipitates is an effective strategy for achieving superior mechanical performance.